a) Field of the Invention
This invention relates to a shift lever assembly for a transmission, which shift lever assembly has realized precise engagement between a control finger and shift lugs in a gear position selector mechanism.
b) Description of the Related Art
Manually shifted automobile transmissions are provided with a shift lever assembly. Shift lever assemblies have conventionally included those provided with two fork shafts (shift rails) and those equipped with three fork shafts.
A shift lever assembly with two fork shafts is arranged, for example, as an indirectly operated shift lever assembly with a shift lever disposed on a column portion of a steering wheel and is employed in association with a 3-forward/1-reverse transmission in which the first fork shaft is for the 1st range and the reverse range and the second fork shaft is for the 2nd and 3rd ranges.
A shift lever assembly with three fork shafts, on the other hand, is arranged as a directly operated shift lever assembly with a shift lever arranged on a floor and is employed in association with a 4-forward/ 1-reverse transmission in which the first fork shaft is for the 1st and 2nd ranges, the second fork shaft is for the 3rd and 4th ranges, and the third fork shaft is for the reverse range or as a 5-forward/1reverse in which the third fork shaft is for the fifth range and the reverse range.
Whichever the shift lever assembly may be, individual fork shafts are provided at predetermined positions with shift forks (gear shift forks), respectively, and also at basal end portions (at one end portions) thereof with shift lugs in an adjacent relationship. A control finger disposed at a free end portion of a shift lever is brought into engagement with one of the shift lugs to select the fork shaft to be slidingly shifted.
FIG. 11 illustrates one example of a conventional shift lever assembly equipped with three fork shafts. Three shifting fork shafts 1,2,3 are arranged in parallel with each other and at one end portion of the respective fork shafts 1,2,3, shift lugs 4,5,6 are arranged adjacent each other.
The individual shift lugs 4,5,6 are provided with pockets 4a, 5a, 6a, respectively, so that the pockets 4a, 5a, 6a are communicated with each other. In the pockets 4a, 5a, 6a so communicating, a free end portion of a control finger 7 is fitted.
Further, the fork shafts 1,2,3 are provided with shift forks 9,10, respectively (note: the third shift fork is not shown).
Because of such a construction, operation of a shift lever 8 causes the control finger 7 to move in the pockets (4a, 5a, 6a) so that the control finger 7 is selectively brought into engagement with one of the shift lugs 4,5,6. The thus-selected one of the fork shafts 1,2,3 is axially moved forward or rearward (shifted), whereby sliding gears and counter gears of the transmission are selectively connected together or a shift sleeve of a synchromesh gear mechanism is caused to slide to achieve a desired gear position.
Although not clearly envisaged from FIG. 11, the shift lugs 4,5,6 and the control finger 7 are chamfered at mutually-contacting corner portions as shown in FIGS. 5 and 9 to improve the shift feeling of the control finger 7.
The above conventional shift lever assembly is however accompanied by the problem that when the control finger 7 is shifted at a position between two adjacent shift lugs to perform a gear shift, the control finger 7 may enter between the shift lugs to produce wedging force and this wedging force then acts to bend components and to widen the distance between the shift lugs beyond a tolerance, whereby the control finger 7 is fitted in between the shift lugs, for example between shift lugs 5,6 (or 4,6) as shown in FIGS. 6 and 10 and shifting operation becomes no longer feasible.
The above problem occurs especially because wedging forces as a result of an attempted entry of the control finger 7 between the shift lugs 5,6 (or 4,6) act on the shift forks 9,10 via the fork shafts 2,3 (or 2,1), causing the shift forks to flex. The fork shafts are then forced to turn to the extent corresponding to the flexions of the shift forks, respectively, and the shift lugs are consequently forced to turn.
This problem occurs more markedly as the lengths of the shift forks become longer, for example because of the adoption of a larger transmission.